Refactored Numbers Spelling kata in Clojure

I've refactored the Numbers Spelling kata I recently did in Clojure to remove some duplication.

Before refactoring it, I had to make the old spell-out-number-over-99 and spell-out-number-up-to-99 functions similar enough for the duplication pattern to emerge.

Then I could use the same function for both cases and also made some other minor changes such as using when-not form and renaming several bindings and arguments.

This is the refactored code:

	(ns number-spelling.core)
	(declare
	one-word-numbers
	num-digits
	pow
	number-spelling)
	(defn spell-out [number]
	(if-let [one-word-number (get one-word-numbers number)]
	one-word-number
	(let [num-digits (num-digits number)]
	(cond
	(> num-digits 9)
	(number-spelling number 1 9 " billion" ", ")
	(> num-digits 6)
	(number-spelling number 1 6 " million" ", ")
	(> num-digits 3)
	(number-spelling number 1 3 " thousand" ", ")
	(> num-digits 2)
	(number-spelling number 1 2 " hundred" " and ")
	:else
	(number-spelling number 10 1 "" " ")))))
	(defn- number-spelling [number factor exp separator1 separator2]
	(let [power-of-ten (pow 10 exp)
	close-number (* factor (quot number power-of-ten))
	rest-of-number (rem number power-of-ten)]
	(str (spell-out close-number)
	separator1
	(when-not (zero? rest-of-number)
	(str separator2 (spell-out rest-of-number))))))
	(defn- pow [base exp]
	(reduce * (repeat exp base)))
	(defn- num-digits [number]
	(count (str number)))
	(def ^:private one-word-numbers
	{0 "zero"
	1 "one"
	2 "two"
	3 "three"
	4 "four"
	5 "five"
	6 "six"
	7 "seven"
	8 "eight"
	9 "nine"
	10 "ten"
	11 "eleven"
	12 "twelve"
	13 "thirteen"
	14 "fourteen"
	15 "fifteen"
	16 "sixteen"
	17 "seventeen"
	18 "eightteen"
	19 "nineteen"
	20 "twenty"
	30 "thirty"
	40 "forty"
	50 "fifty"
	60 "sixty"
	70 "seventy"
	80 "eighty"
	90 "ninety"})

view raw number-spelling-refactored.clj hosted with ❤ by GitHub

You can find the code in this repository in GitHub.